You know that the evolution of computer started from 16th century and resulted in the form that we see today. The present day computer, however, has also undergone rapid change during the last fifty years. This period, during which the evolution of computer took place, can be divided into five distinct phases known as Generations of Computers. Each phase is distinguished from others on the basis of the type of switching circuits used. First Generation ComputersFirst generation computers used Thermion valves. These computers were large in size and writing programs on them was difficult. Some of the computers of this generation were: